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Active ingredient

Sildenafil

Sildenafil is the active ingredient in a group of medicines used to treat erectile dysfunction in adult men. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. It is the generic equivalent of the originally branded medicine Viagra. It is used to help men who have difficulty achieving or maintaining an erection sufficient for sexual activity.

Reviewed by the Kam4eu editorial team on 13 August 2026 · Next review August 2027

Sildenafil medicines we deliver

Browse the full Erectile Dysfunction range

23 generic Sildenafil products — same molecule, different brands, formats and pack sizes.

How it works

Sildenafil works by blocking the PDE5 enzyme, which allows levels of a substance called cyclic guanosine monophosphate (cGMP) to rise in the tissues of the penis. This helps relax the blood vessels and improve blood flow when a man is sexually stimulated. Sexual arousal is still needed for the medicine to take effect; it does not cause an erection on its own. It generally begins to work within roughly half an hour to an hour and its effect usually lasts for a few hours.

How it is taken

Sildenafil is normally taken by mouth a short time before planned sexual activity, at the dose advised by your doctor. It can be taken with or without food, although a heavy or high-fat meal may delay how quickly it starts to work. As a general rule no more than one dose should be taken in any 24-hour period. Always follow the instructions in the patient information leaflet and the advice of your doctor or pharmacist.

Side effects

Common (usually mild and temporary):

  • Headache
  • Flushing of the face
  • Indigestion or stomach upset
  • Nasal congestion (blocked or runny nose)
  • Dizziness
  • Changes in vision such as a blue tinge or blurring

Stop and seek medical help if you experience:

  • A painful erection lasting longer than 4 hours (priapism) — seek urgent medical help
  • Sudden loss or decrease in vision in one or both eyes
  • Sudden loss or reduction in hearing, sometimes with ringing in the ears
  • Chest pain during or after sexual activity
  • Signs of a serious allergic reaction such as swelling of the face, lips or throat, rash or difficulty breathing

Safety & who should not take it

  • Must NOT be taken with nitrate medicines (used for chest pain/angina) or nitric-oxide donors such as amyl nitrite 'poppers', as this can cause a dangerous drop in blood pressure.
  • Use with caution if you have heart or blood-vessel disease, or if sexual activity has been advised against for heart reasons.
  • Tell your doctor about any liver or kidney problems, as a dose adjustment may be needed.
  • Caution is needed if you have low blood pressure or take alpha-blockers or other blood-pressure-lowering medicines.
  • Drinking alcohol can lower blood pressure further and may reduce the medicine's effectiveness.
  • Grapefruit and grapefruit juice may affect how the medicine works and are best avoided.
  • Not intended for use by women, children or anyone under 18 years of age.

Storage

Store in the original packaging below 30°C, out of the sight and reach of children, and do not use after the expiry date.

Frequently asked questions

How long does sildenafil take to work?+

It typically begins to work within around 30 to 60 minutes of being taken, though this can vary between individuals and may be delayed by a heavy meal. Check the patient information leaflet for guidance.

Can I take it with food?+

It can be taken with or without food, but a large or high-fat meal may delay the onset of its effect. Your doctor or pharmacist can advise on timing.

How is sildenafil different from Viagra?+

Sildenafil is the active ingredient and the generic equivalent of the branded medicine Viagra; both contain the same active substance and work in the same way.

Important: This information is general and not a substitute for medical advice. Always read the patient information leaflet supplied with your medicine and consult a doctor or pharmacist before use — especially if you have existing health conditions or take other medication.

Sildenafil health guides

“Liquid Viagra”: What People Actually Mean — and the Real Options

Summary: there is no official product called “liquid Viagra” — the phrase is what people search when they want sildenafil in a form that isn’t a hard tablet to swallow. The real options that fit that idea are effervescent (dissolvable) tablets you drink and oral jelly sachets, both of which deliver the same active ingredient, sildenafil, as a standard tablet. This guide explains what “liquid Viagra” really refers to, how the dissolvable and jelly formats compare, that the format changes convenience rather than strength, and the safety rules that stay the same whichever form you choose.

Read guide

The “Blue Salt Trick” for ED: Does It Actually Work?

Summary: the viral “blue salt trick” — a supposed at-home mix said to work like Viagra — has no clinical evidence behind it, no defined recipe, and no plausible mechanism for improving blood flow the way erectile dysfunction actually requires. It is internet folklore, not medicine. This guide explains where the trend came from, why salt cannot do what a PDE5 inhibitor does, the real (small) role salt plays in vascular health, and the evidence-based options — like sildenafil and tadalafil — that a doctor or pharmacist can help you use safely.

Read guide

Why generic sildenafil and Cialis have 20 brand names

Summary: Kamagra, Cenforce, Fildena, Sildamax, Suhagra and Silagra are all sildenafil. Vidalista, Tadalista and Tadaga are all tadalafil. The molecule is identical and off-patent; the brand name only tells you which manufacturer made it and in what format. Here's how to read a generic name, why the prices differ anyway, and which differences actually matter.

Read guide

How to get a Viagra prescription: every legitimate route

Summary: In the EU and EEA, sildenafil is a prescription-only medicine, and there are three legitimate ways to get that prescription — your own family doctor, a specialist such as a urologist, or a licensed telemedicine service. A prescription from a doctor in one EU country is valid in the others. This guide covers what you'll actually be asked, what it costs, and what makes someone ineligible.

Read guide

Related conditions & treatments

Conditions Sildenafil treats

Erectile Dysfunction Premature Ejaculation

Other treatments for the same conditions

TadalafilVardenafilAvanafilDapoxetine

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